Method and means for drying accumulator electrodes



May 22, 1956 E. G. SUNDBERG ET AL METHOD AND MEANS FOR DRYINGACCUMULATOR ELECTRODES Filed Jan. 5, 1954 2 Sheets-Sheet 1 E Gus-rpmswosezn Baal: GuruNAQOUsQA N Vi N TORS ml-1 ATTH s y 1956 E. G. SUNDBERGET AL 2,747,008

METHOD AND MEANS FOR DRYING ACCUMULATOR ELECTRODES Filed Jan. 5, 1954 2Sheets-Sheet 2 III W I H ll] [III] 5 g GUNNAR o BRcK F47. Em GUSTAVSUNDBERG B) mm mm Rud- TT' S.

United States Patent METHOD AND MEANS FOR DRYING ACCUMULATOR ELECTRODESErik Gustav Sundberg, Osbacken, N01, and Bror Gunnar Ousbiick, Goteborg,Sweden, assiguors to Aktiebolaget Tudor, Stockholm, Sweden, :1 Swedishjoint-stock com- P y Application January 5, 1954, Serial No. 402,333

Claims priority, application Sweden May 21, 1952 12 Claims. (Cl. 136-33)The present application is a continuation-in-part of our formerlycopending application, Serial No. 354,824 filed May 13, 1953, for Methodand Means for Drying Battery Electrodes, which application is nowabandoned.

In the manufacture of lead accumulators each separate plate, thenegative as well as the positive, must be subjected to an electrolyticforming treatment in order to attain the electrochemical characteristicsnecessary for the accumulator. For certain types of batteries the laststage of the forming involves charging and treating of the plates sothat after the final treatment the discharge capacity of the platesamounts to the value which may be obtained in a battery in normaloperation when in fully charged condition. A battery made of platescharged in this manner and suitably dried can be stored during apractically unlimited time with its charge preserved so that even aftera long time in storage the battery can be made ready for immediate usemerely by filling it with electrolyte. However, it is a prerequisitethat the plates shall not be permitted to be attacked by air, acids,moisture etc. while in storage. Therefore, the plates must either bestored with the container effectively hermetically sealed or the platesmust be given a final treatment in such that sufiiciently effectiveprotection against destruction is obtained.

An especially important step in the manufacture of charged plates is thedrying of the plates after the electroforming and the usual washing inconnection therewith.

In general, the invention utilizes method steps which cause displacementof the water from the formed porous electrode and from the separators ifcomplete storage battery electrode assemblies are involved. Thedisplacement of the water is produced by means of a treatment liquid.The treatment liquid is thereafter evaporated from the electrode andpreferably, the treatment liquid is such character that a thinprotective coating remains on the electrode. This protective coatingprevents deterioration of the electrodes while the fully charged newbattery is not used and avoids the necessity for hermetically sealingthe battery case prior to filling it with electrolyte at the time whenit is originally placed in service.

The invention further comprises apparatus adapted to perform thesemethod steps with a maximum economy of treatment liquid and heat.

The main principle for drying accumulator electrodes according to theinvention is broadly characterized by the fact, that the Water retainedby the electrodes to be dried is replaced by a treatment liquid otherthan water and that the treatment liquid is subsequently caused toevaporate. Since the treatment liquid requires a much smaller amount ofheat its evaporation than the water, the drying process is materiallyfacilitated by this replacement. The invention is also useful where itis desired to dry and treat assembled electrode groups comprisingpositive and negative electrodes as well as separators. The separatorsmay then be dried at the same time as the electrodes of the groupsthrough a replacement of the water by the treatment liquid andsubsequent evaporation of the latter.

The replacement of the water can be carried out in different waysdepending on the particular structure involved, for example, if onlynegative electrodes, if positive and negative electrodes, or if completegroups consisting of positive and negative electrodes and separators areto be dried. In the examples given below dilferent liquids and differenttemperatures are used and it can be preferable to use one method or theother depending for instance, upon the material the separators are madeof. When only negative electrodes are dried, the treatment can becarried out at a higher temperature than when positive electrodes arealso dried at the same time.

The replacement of the Water may for example be carried out by bringingthe electrode into contact with the treatment liquid, the treatmentliquid being brought to or maintained at a temperature suificiently highto cause the water to evaporate. Preferably, the temperature is sochosen that either the treatment liquid or the Water retained in theelectrode or both are caused to boil.

This contact with the treatment liquid may conveniently be brought aboutby placing the electrodes to be dried in a vessel containing orreceiving the treatment liquid and by supplying heat to the vessel inorder to maintain the required temperature during the drying process.

The treatment liquid thus constitutes a medium for supplying heat to thewater retained in the electrode and after having replaced the water thetreatment liquid may be very easily driven off. The final drying whichremoves the treatment liquid from the electrode after it has replacedthe water is inherently accelerated by the heat stored in the electrode.This final drying may be further accelerated by the use of reducedpressure or by the forced circulation of a gas such as air or nitrogenaround the' electrode.

In order that a sufficiently complete substitution of the treatmentliquid for the water shall be readily achieved and furthermore, that thetreatment liquid may be readily separated from the water and, recoveredfor re-use, it is convenient to use a treatment liquid, which isinsoluble or only slightly soluble in water.

It is possible to use a treatment liquid which has a lower boiling pointthan water. As is well known in connection with distillation processesthe treatment liquid will carry away a certain fraction of water duringits evaporation. The maximum temperature will then be limited by thedifference between the boiling point of the treatment liquid and theboiling point of the water. This will be the case if, for instance,petrol, gasoline, or heptane is used as the treatment liquid. Since itthen is necessary that the treatment liquid shall boil, a comparablylarge amount of treatment liquid will be evaporated along with thewater.

Even though the treatment liquid vapor is recovered by means of a returncondenser, the comparatively great turnover of the treatment liquid willcause certain heat losses, but on the other hand, the process may becarried out at a comparably low temperature and the final driving off ofthe treatment liquid will be facilitated, whereby the said heat lossesare more or less compensated for.

For purposes of heat economy it is preferable to use a treatment liquid,the boiling point of which is higher than that of water. The temperatureis then chosen so that the water boils away while the boiling point ofthe treatment liquid is not reached. In practice it is often desirableto use a liquid consisting of a mixture of several components as will bedescribed hereinafter, and in such a case at least the dominatingcomponent or components should have boiling points which are higher thanthat of water. As used hereinafter, the term boiling point of thetreatment liquid is intended to refer to the boiling point of thedominant component or components in the case of a treatment liquid whichconsists of a mixture of several components.

In this way a considerably smaller amount of treatment liquid is carriedaway with the water. If atmospheric pressure is maintained, thetemperature is inherently kept substantially at 100 C. as long as anyconsiderable amount of water remains in the electrode, because theboiling point of the water then determines the maximum temperature. Whenthe water has been driven off, the temperature of the treatment liquidstarts to rise and the heat supply should preferably be controlled sothat the boiling point of the treatment liquid will not be reached. Bychoosing a treatment liquid the boiling point of which is considerablyhigher than the boiling point of water and controlling the heat supplyso as to raise the temperature after the water has been driven off to apoint slightly below the treatment liquid boiling point, and of coursealso below the softening point of the electrode material, a sutficientamount of heat may be stored in the electrodes so that the treatmentliquid evaporates in a very short time upon removal of the electrodefrom the treatment liquid bath or vice versa.

The final drying may also, with or without a final increase oftemperature, be accelerated by reducing the pressure acting on theelectrodes, whereby the vaporization of the treatment liquid remainingon the electrodes will be promoted. As will be described hereinafter,kerosene may conveniently be used as treatment liquid, and it is thensuitable to control the heat supply to the bath so that the temperaturerises to about 150 C. at the end of the process.

In order to obtain a protective layer on the electrodes remaining afterthe drying process, a liquid may be used embodying one or morenon-volatile or at least less volatile components than the kerosenementioned above as an example. Other treatment liquids of this class areturpentine and petrol or gasoline. It is also possible to admix in thetreatment liquid a quantity of a non-volatile substance, or acombination of such substances, especially in the event that thetreatment liquid itself has not such physical properties that aremaining protective coating can be obtained. Examples of such treatmentliquids are benzene or light hydrocarbons belonging to the aliphaticseries such as heptane or octane which are stable compounds With butslight chemical activity towards the material of battery electrodes andseparators. The admixed substance or substances should be easily brokendown by the electrolyte in which the electrodes are immersed foroperation, or the quantity of such substance or substances should be soslight that it does not adversely affect the properties of theelectrodes and separators.

As examples of suitable admixed substances parafiin oil, castor oil andyolk (also called suint, an unctuous secretion of the skin of sheep) maybe mentioned although many other substances selected for instance theclasses mineral oils, animal fats, vegetable oils, waxes and natural orsynthetic resins may be useful. The protective coating may also beeffected by admixing in the treatment liquid one or more polymerizablesubstances, which are caused to polymerize during the heat treatment'for the final drying or by means of a special heat treatment. Theadmixed substance or substances should be soluble in the treatmentliquid, but insoluble in water.

In order to diminish the tire hazard it is also possible to use anon-combustible treatment liquid, e. g. belonging to the class ofchlorinated hydrocarbons such as carbon tetrachloride, trichlorethyleneor perchlorethylene, with or without the admixture of one or moresubstances for forming a protective coating on the electrodes ashereinbefore described.

The main characteristic of the method described above for effectingreplacement of the water by the treatment liquid is that the water isvaporized whereas the treatment liquid remains and is absorbed by theelectrodes. There are, however, also other methods for effecting thedesired replacement.

Thus, for instance, a treatment liquid may be used having so small asurface tension that it displaces the water mechanically due to therelatively greater adhesion to the electrode material of the treatmentliquid. In this case it is not necessary to supply heat for carrying outthe process, although an increase of temperature of the treatment liquidmay be advantageous as it accelerates the process. Any treatment liquidproperly chemically inactive to the material of the electrodes andlikewise to the separators if complete electrode groups with separatorsare treated may be used with or without the admixture of suitablesurface tension modifying agent such as an emulsifying agent or wettingagent. For instance, as in the case of treatment liquids which areinsoluble or only slightly soluble in water and mentioned as examplesabove, heat ing may also be used in this case. The wetting oremulsifying agent, if any, may preferably be soluble in the treatmentliquid and insoluble in Water. The emulsifying or wetting agent admixedin the treatment liquid should of course also be substantially inactivechemically towards the material of the electrodes and separators and,furthermore, it should preferably not be of a type which forms foam. Thetension modifying agent may for instance be a compound of the classcomprising naphthenic acids. Also a mixture of several tension modifyingagents may be used. There are many emulsifying and wetting agentsavailable in the market and some of them are adapted for use withcertain treatment liquids. The exact compositions of such substances areusually kept secret by the manufacturers, and the most suitable surfacetension modifying agent for use with a particular treatment liquid mustordinarily be determined experimentally.

Also in the event that the treatment liquid may contain one or morenon-volatile or slightly volatile substances or one or more suchsubstances may be admixed with it for forming a protective coating ashas already been described in connection with the heating method.

In order to facilitate the final drying, that is the removal of thetreatment liquid, it is preferable to use an easily relatively volatiletreatment liquid, such as hydrocarbons of the aliphatic series, forexample heptane (C7H16), whereby the final drying may be effectedwithout any supply of heat, although it will be understood that anincrease of temperature will always expedite the final drying process.

A common feature of the two methods described above for replacing thewater retained in the electrodes by a treatment liquid is that thetreatment liquid in both cases is preferably insoluble or only slightlysoluble in water.

A third method for eifecting replacement of the water is the use of atreatment liquid which dissolves the water out of the electrode. Thetreatment liquid then forms a solution with the water retained in theelectrode and the supply of treatment liquid should be suificient sothat the final concentration of water will be very slight andimmaterial. It will be understood that the treatment liquid preferablyshould initially be free from water. Conyeniently, the treatment liquidis then circulated in a closed circuit comprising a still or a filterfor continuously refining the treatment liquid and freeing it fromwater. Such a filter may for instance contain quicklime or some otherknown dehydrating agent which is suitable for use in refining andconcentrating hygroscopic liquids. Acetone and alcohol may be mentionedas examples of treatment liquids of this class, which compounds arerelatively volatile, whereby the final drying will be quickly and easilycompleted. The whole process may be carried out at room temperature, butit will be understood that an increase of temperature, particularlyduring the final drying, will accelerate the process.

Also in this case the treatment liquid may contain one or morenon-volatile or slightly volatile substances for forming a residualprotective coating on the electrode. The coating substance or substancesshould be soluble in the treatment liquid but insoluble or only slightlysoluble in water and the same additional substances set forth above inconnection with the purely thermal method are also suitable for use inthis modified method.

The invention will be more fully understood by' reference to theaccompanying drawing together with the following description.

Referring to the drawing:

Figure 1 is a diagrammatic elevational view of apparatus for carryingout the method described above by the use of heating means.

Figure 2 is a view similar to Fig. 1 in which the method is carried outsubstantially at room temperature.

Referring to Fig. l, the reference numeral 1 designates a treatmentvessel having heat insulated walls 2 and a top lid 3, likewise heatinsulated. In the vessel numeral one (1) there are horizontal supportingbars 4 for supporting the battery plates 5 to be treated, and the lid 3is hinged or removable, so that the treatment vessel can be opened whenbeing loaded with plates, the lid 3 being closed during operation.Numerals 6 and 7 designate inlets and outlets respectively of heatingpipe loops (not otherwise shown) which provided at the bottom of thevessel for heating the treatment liquid by means of superheated steam orthe like supplied to the pipe loops from a suitable source. It is alsopossible to supply the pipe loops with some other heating medium such ashot oil which transfers heat from an electrical or other heat source.

The other main parts of the plant shown are a supply vessel or storagetank 8, a condenser 9, a cyclone separator 10, a suction fan 11, aseparation tank 12 and conduits lit-24- controlled by valves 13v22vrespectively.

The operation of the plant will be understood from the followingdescription of an operation cycle for carrying out the process.

At the beginning of the process the treatment vessel 1 is empty. Alsoseparation tank 12 may be assumed to be empty. All the valves shown inFig. 1 of the drawing may then be presumed to be in closed position.After the battery plates 5 have been placed on the supporting bars 4 andthe lid 3 has been closed, valves 13v and 141 are opened. Conduit 13,which debouches into the top portion of supply vessel 3, is connected toa source of compressed air (not shown) and due to the increased pressureon the surface of the treatment liquid 25, which here is presumed to bekerosene, petroleum, or photogene, the treatment liquid is forcedupwardly through conduit 14 extending from the bottom of supply vessel 8into the treatment vessel 1. When the separation tank 12 has beenentirely filled through conduit 15 and then treatment vessel 1 has beenfilled to a predetermined level with kerosene 25 valves 13v and 14v areclosed. Heat is now supplied to the heating loops indicated at 6 and 7.When the kerosene bath 25 in vessel 1 reaches a temperature of about 100C., the water retained in the plates 5 commences boiling. During theboiling the water evaporates through conduit 16 into condenser 9, whichis provided with cooling pipe loops or the like in a conventional manner(not shown). The evaporated steam carries with it a certain amount ofkerosene which is condensed or collected along with the steam from theplates in condenser 9. Although the boiling point of the kerosene hasnot been reached, it is in most cases not possible or necessary toprevent some amount of kerosene from being transferred to the condenser0, and some volatile components of it may evaporate and be condensed incondenser 9 even before the temperature of the treatment liquid hasreached the boiling point of the water retained in the plates. Thecondensed water and the kerosene or kerosene components runs down intothe separation tank 12 through conduits 17 and 18. The separation tank12 should be large enough to hold the amount or" water contained in atleast one batch of plates in treatment vessel 1.

In the separation tank 12 the condensate running down from condenser 9will be separated into water and kerosene or kerosene components, sincethe water, having the greatest specific gravity, sinks to the bottom,while the kerosene with its components floats on the water. The waterand the kerosene in tank 12 are designated 26 and 25 respectively. Sincethe water evaporated from the plates in vessel 1 will in this way beretained Within the system, the level of the treatment liquid in vessel1 will be substantially unchanged during the process.

As long as there remains any considerable amount of water in the plates5 the heat supplied to vessel 1 will be almost entirely consumed forgenerating steam, and thus the temperature will not rise appreciablyabove the boiling point of the water in the plates, that is above aboutC. in case the treatment is carried out at atmospheric pressure.

At the end of the drying process when the water or the major part of ithas boiled away from the plates and has been replaced by kerosene, thetemperature begins to rise. When it has reached a value preferablyconsiderably higher than the boiling point of water but preferably belowthe boiling point of the dominating components of the kerosene, sayabout C., the heat supply at 6 and '7 to vessel 1 is interrupted. Thewater 26 collected in separation tank 12 is let out through valve 19v ofdischarge conduit 19.

When all the water 26 has been removed, valve 19v is closed and valves20v and 21v are opened, so that the treatment liquid runs back into thesupply vessel 8 through conduit 29, while the air above the surface ofthe kerosene in supply vessel 8 escapes through conduit 21. This processmay of course be accelerated by means of a pump or by compressed airsupplied to the upper space of vessel 1 and a valve must then beprovided in conduit 16 and closed temporarily while vessel 1 is underpressure.

The fan 11 is now put into operation, whereby air is sucked throughconduit 22, vessel 1, conduit 16, condenser 9, conduit 23, cycloneseparator 10 to suction fan 11. Due to the great amount of heat storedin the plates 5 through the final increase of temperature, the main partof the kerosene retained by the plates 5 rapidly evaporates. The leastvolatile component or components of the kerosene, however will beretained by the plates, said component or components forming a thincoating effectively protecting the material of the plates against attackfrom gases as well as from the humidity of the atmosphere.

The kerosene gases evaporated from the plates are condensedsubstantially in condenser 9 and the condensate runs back into supplyvessel 8 via conduits 17 and 18, separation vessel 12 and conduit 20.Some liquid particles may, however, be sucked with the air streamtowards suction fan 11. Conduit 23 debouches tangentially into cycloneseparator 10 in a manner well known in such separators, whereby theliquid particles are thrown out radially against the wall of the cycloneseparator and run down through conduits 24 and 18 to separation tank 12and via conduit 20 back to supply vessel 8 as described. Also anyremaining amount of vapour will be condensed in cyclone separator 10 dueto the expansion occuring in the same. The losses of treatment liquidmay thus be kept low.

When the final drying is finished, the suction fan 11 is stopped and theplates 5 are removed and placed, for instance, in their ordinary batterycasings, in which they can be stored for years without electrolyte andalso without any requirement of hermetically sealing the casings.

It will be readily understood that the apparatus of Fig. 1 will operatein substantially the same way regardless of which treatment liquid isused. If the boiling point of the treatment liquid, petrol for instance,is lower than that of water, it will be appreciated that a greateramount of treatment liquid will circulate through the system and thatany final temperature rise for the final drying cannot be so easilyeffected, but in point of principle the plant may be used with advantagefor all treatment liquids mentioned or indicated in the foregoingspecification.

It has been found to be desirable that the electrodes shall be exposedto the air for as short a time as possible during the interval betweenthe electroforming and the treatment according to the invention. Forthis reason it may be advantageous to keep the electrodes in a waterbath until the treatment begins. Thus for instance it is possible eitherto initially fill the treatment vessel with water and immerse theelectrodes in the water bath or have the electrodes placed in a specialwater container which is in turn placed in the empty treatment vessel,whereupon the treatment liquid is caused to replace the water at thesame time as it fills the treatment vessel.

The reason Why conduit 14 for supplying the treatment liquid totreatment vessel 1 debouches at the top of this vessel is to make itpossible for the treatment vessel 1 to be initially filled with waterthrough a conduit (not shown), the water being continuously let outthrough valve 19v as the treatment liquid fills the treatment vessel 1and separation tank 12 from above, so that the plates 5 are all the timekept below the liquid level. It will be appreciated, that in the casethe treatment vessel 1 is not initially filled with water, that conduit14 may be dispensed With, provided conduit 20 then extends to the bottomof supply vessel 8. Conduit 219 is then used for supplying treatmentliquid to separation tank 12 and treatment vessel 1 at the beginning ofthe process as Well as for returning it to the supply vessel at the endof the process.

It will be understood that the plant shown in Fig. 1 may be used withoutany or only slight modifications for a treatment liquid having a surfacetension modifying agent admixed therein for replacing the water retainedin the plates. The heating pipe loops or corresponding heating means maythen be dispensed with although they also may be retained and used foraccelerating the process by a moderate increase of temperature.

As has already been mentioned it is also possible to combine diiferentmethods for replacing the water retained in the plates or plates andseparators respectively by the treatment liquid. Such a combination maybe justified, for instance, in the case one method is particularlysimple and economical with regard to separators, heat consumption,refinement of the treatment liquid etc. but does not quitesatisfactorily free the plates and separators from water in a moderatetime of treatment, While another method is capable of removing the watermore completely but on the other hand is not suitable for removing allthe water. The main part of the water is then conveniently removed bythe first-mentioned method, so that only a comparably slight amount ofwater remains in the plates or separators after this treatment, whilethe removal of the remainder is effected by the last-mentioned method.

In Fig. 2 a plant is shown which is adapted for such a combined processcomprising a first treatment with a treatment liquid insoluble in waterand having a surface tension modifying agent admixed therewith, and asecond treatment with a treatment liquid soluble in water and removingthe residual water still remaining after the first treatment bydissolving the residual water out of the plates.

All elements in Fig. 2 which are identical or similar to correspondingelements in Fig. 1 have the same reference numerals as in Fig. 1. Itwill be found that the treatment vessel 1, separation tank 12 and theright-hand part of the plant including supply vessel 8, condenser 9 andsuction fan 11 with their associated conduits are arranged similarly tothe arrangement shown in Fig. l. The cyclone separator of the plantshown in Fig. 1, however, has been replaced by a filter 27, containingactive carbon, and, furthermore, conduit 13 is connected to conduit 14through a pump 28, while conduit 14 is directly connected to the outletconduit 17 of condenser 9 on one hand and to the treatment vessel 1through conduits 29 and 31) on the other hand.

The left-hand part of the plant comprises store tank 31, a still 32, acondenser 33, a filter with active carbon 34, a suction fan 35, a pump36, and conduits 37-43 controlled by valves 38v40v respectively.

The treatment liquid 25a in supply vessel 8 consists for instance ofheptane with a naphthenic acid or an admixed surface tension modifyingagent.

In this case it may be assumed that the treatment vessel 1 is filledwith the treatment liquid 25a before the plates 5 to be dried areimmersed therein.

Before the plant is put into operation all the valves are closed and thetreatment vessel 1 is empty. The filling of the latter with treatmentliquid 25a is effected by opening valves 14v, 29v, 30v, 15v and 13v.Compressed air supplied to conduit 13 presses the treatment liquid 25aupwardly from supply vessel 8 through conduits 14, 29 and 3% into vessel1 and through conduit 15 also into separation tank 12. When tank 12 hasthus been entirely filled and vessel 1 has been filled to apredetermined level, valves 13v and 1411 are closed and the plates 5 areimmersed in the treatment liquid 25a of treatment vessel 1. Due to thereduced tension action of the treat ment liquid 25a the water iscontinuously forced out of the plates and replaced by treatment liquid.The process is promoted by means of a pump 23 causing the treatmentliquid to circulate through a closed path comprising conduits 18, 14, 29and 30, whereby the treatment liquid is propelled through separationtank 12, where the water 26 sinks to the bottom. In this way the mainpart of the water retained in the plates 5 is transferred to theseparation tank 12. The water 26 is now let out through valve 19v andthe treatment liquid is then returned from separation tank 12 and vessel1 to supply vessel 8 through conduit 20 in the same way as has beendescribed in connection with Fig. 1.

It will be appreciated that the treatment liquid may alternatively bereturned to supply vessel 8 by opening valve 14v so that the emptying ofthe vessel 1 is accelerated by pump 28.

The next step is the removal of the treatment liquid 25a from the platesin the treatment vessel 1. Valve 22v is then opened while preferably allof the other valves, except valve 30v, are closed, and suction fan 11 isstarted. Air is sucked through conduit 22, vessel 1, conduit 16,condenser 9 and filter 27, whereby the treatment liquid retained in theplates evaporates and follows the air towards suction fan 11. The mainpart of the evaporated treatment liquid is condensed in condenser 9 andreturned to the system through conduits 17 and 14 While any remaindernot condensed will be absorbed by the filter 27.

The first drying process may be insufficient to remove all orsubstantially all the water from the plates and the drying may then becompleted by means of treatment liquid 25b of supply vessel 31.Treatment liquid 25b preferably consists of acetone or alcohol or asimilar liquid capable of dissolving Water. A non-volatile or slightlyvolatile substance non-insoluble in water is admixed with the treatmentliquid 25b for forming a protective layer on the treated plates as hasalready been described. Valves 38v, 39v and 40v are opened while all theother valves are closed. The pump 36 is started, whereby the treatmentliquid 25b is first caused to fill treatment vessel 1 and then tocirculate in a path comprising conduit 37, pump 36, conduit 38,treatment vessel 1, conduit 40, conduit 39, still 32, conduit 42 andsupply vessel 31. The treatment liquid 25b thus takes up the remainingwater from the plates, which is then separated from the treatment liquidin still 32, keeping the treatment liquid returned to the vessel 31continuously pure or at a high concentration.

When this phase of the process has been continued for a time sufiicientto assure a satisfactory removal of the remaining water from the plates,pump 36 is stopped and the treatment liquid 25b is returned to supplyvessel 31 through conduit 38 or through a special return conduit (notshown). Valve 22v is now opened, valve 39v is closed and suction fan 35is started, whereby air is sucked through conduit 22, treatment vessel1, conduits 40 and 41, condenser 33 and filter 34. The treatment liquid25b retained in the plates is thus evaporized and follows the air streamtowards suction fan 35. The main portion of the evaporated treatmentliquid is condensed in condenser 33 and returned to supply vessel 31through conduit 43 via still 32, in which it is dehydrated. Theremainder of the evaporated treatment liquid is absorbed by filter 34.

Although the processes described in connection with Fig. 2 mayconveniently be carried out at room temperature, it is obvious that alsoin this embodiment the treatment vessel 1 may be provided with means forincreasing the temperature as desired during any or all of the phases ofthe process.

The still 32 is shown in block-form only, as it is a wellknownconventional device constructed and arranged for separating water fromalcohol, acetone etc. through distillation. The still 32 may be replacedby a vessel containing a dehydrating agent, such as quicklime,particularly if a treatment liquid, e. g. alcohol, which is used isincapable of being fully concentrated by distillation. It is alsopossible to insert such a vessel with a dehydrating agent between thestill 32 and the supply vessel 31.

The embodiments of the invention described above are disclosed by way ofexample only, and it will be understood from the foregoing specificationthat the invention may be utilized in many different ways within thescope of the appended claims.

The method according to the invention may be used for treating eitherpositive or negative electrodes or for positive as well as negativeplates at the same time. It is also possible to treat assembledelectrode assemblies comprising separators, and it will be understoodthat the treatment liquid or liquids as well as additional substancesand agents must be chosen with regard to the various conditions. Thus,for instance, the treatment of an electrode assembly comprising rubberseparators should be carried out by means of a treatment liquidcomprising admixtures, if any, such that the treatment liquid will notappreciably dissolve rubber. In such a case heptane may be used with anadmixture of an aliphatic fat for forming the protective coating on theelectrodes.

It will also be understood that the method according to the inventionmay be used for treating other electrodes than those for batteries ofthe lead-acid-type, for instance sintered electrodes for alkaline cells.

We claim:

1. Drying apparatus for removing water from a charged porous batteryelectrode, said apparatus comprising in combination: a treatment vesseladapted to contain a treatment liquid which is lighter than water andsubstantially insoluble therein; supporting means disposed in saidvessel and adapted to support said electrode immersed in said treatmentliquid; a separation tank disposed beneath said treatment vessel and incommunication therewith, said treatment vessel having a capacity atleast suificient to hold all of the water removed from said electrode; asupply vessel of treatment liquid; means for transferring treatmentliquid from said supply vessel to said treatment vessel; means forcausing evaporation of treatment liquid in said treatment vessel alongwith water from said electrode; condenser means connected with saidtreatment vessel for receiving vapor therefrom; duct means fortransferring condensate from said condenser to said separation tank;means for removing water from the lower portion of said separation tankand further duct means for returning treatment liquid from saidseparation tank and from said treatment vessel to said supply vessel.

2. Drying apparatus for removing water from a charged porous batteryelectrode, said apparatus comprising in combination: a treatment vesseladapted to contain a treatment liquid; supporting means disposed in saidvessel and adapted to support said electrode immersed in said treatmentliquid; a separation tank disposed beneath said treatment vessel and incommunication therewith; a first supply vessel for a first treatmentliquid, said first treatment liquid being both volatile andsubstantially insoluble in water, said first treatment liquid containinga wetting agent and having a specific gravity less than that of Water; asecond supply vessel for a second treatment liquid, said secondtreatment liquid being both volatile and Water soluble; means fortransferring said first treatment liquid from said first supply vesselto said treatment vessel to displace said water from said electrode;means for circulating said first treatment liquid through said treatmentvessel and said separation tank in a closed circuit; means connectingsaid treatment vessel with said first supply vessel for returning saidfirst treatment liquid thereto; a first air circulating means connectedwith said treatment vessel for circulating air therethrough to evaporatesubstantially all of said first treatment liquid remaining in and onsaid electrode; means connected with said first air circulation meansfor collecting and condensing the vapors of said displaced water andsaid first treatment liquid and conveying the condensate to saidseparation tank; means for transferring said second treatment liquidfrom said second supply vessel to said treatment vessel to dissolveremaining water from said electrode; means connecting said treatmentvessel with said second supply vessel for returning said secondtreatment liquid thereto; and a second air circulating means connectedwith said treatment vessel for circulating air therethrough to evaporatesubstantially all of said second treatment liquid together with thewater dissolved therein remaining in and on said electrode.

3. Apparatus according to claim 2, further comprising condenser meansconnected to said treatment vessel and included in said connection ofsaid second air circulation means thereto for condensing water vapor andvapor of said second treatment liquid; and a still connected to receivecondensate from said condensing means for separating said secondtreatment liquid from said water, said still being connected to saidsecond supply vessel to return a distillate comprising said secondtreatment liquid thereto.

4. The method of drying and protecting a water containing porouselectrode, which comprises the steps of: bringing the electrode to bedried into intimate contact with a first treatment liquid which issubstantially insoluble in water and which includes a wetting agent,said wetting agent being substantially insoluble in water and soluble insaid first treatment liquid for forcing the water out of the electrode,evaporating substantially all of the first treatment liquid retained inthe electrode, bringing the electrode into intimate contact with asecond, water-soluble treatment liquid, including at least oneeifectively nonvolatile coating substance substantially insoluble inwater admixed therein, said second treatment liquid dissolving out ofthe electrode substantially all of the water remaining therein, andevaporating substantially all of said second treatment liquid retainedin the electrode leaving a protective coating on the electrode formed bysaid coating substance.

5. The method of drying a charged battery electrode and simultaneouslyprotecting it against attack from the oxygen of the atmosphere,comprising the steps of: immersing the electrode in a treatment liquidhaving a boiling point higher than that of water and which issubstantially insoluble in water, and including a substantiallynonvolatile coating substance dissolved therein, supplying heat to saidtreatment liquid so as to cause the water of the electrode to evaporate,and evaporating said treatment liquid so as to leave a thin protectivecoating of said coating substance on said electrode.

6. The method according to claim 5, in which a wetting agent soluble inthe treatment liquid and substantially insoluble in water is added tothe treatment liquid.

7. The method according to claim 5, comprising the further steps of:collecting and condensing the vapor of said treatment liquid during theevaporation thereof, whereby said treatment liquid is recovered forre-use.

8. The method of drying a water containing porous charged batteryelectrode and simultaneously protecting it against attack from theoxygen of the atmosphere, com prising the steps of: immersing theelectrode in a treatment liquid which is substantially insoluble inwater, said liquid having a boiling point higher than that of water andincluding an effectively non-volatile coating substance dissolvedtherein, which coating substance is substantially insoluble in water,supplying heat to said treatment liquid so as to cause the water in theelectrode to boil away; terminating contact between said treatmentliquid and said electrode; and causing the portion of the said treatment liquid absorbed by said electrode to evaporate so as to leave athin protective coating of said coating substance on said electrode.

9. The method according to claim 8, comprising the further steps of:collecting and condensing the vapor of said treatment liquid during theevaporation thereof, whereby said treatment liquid is recovered forre-use.

10. The method of drying a water-containing, charged porous batteryelectrode while simultaneously protecting the electrode against attackfrom the oxygen of the atmosphere, comprising the steps of: immersingsaid electrode in a treatment liquid having a boiling point higher thanthat of water, a specific gravity less than that of water, and which issubstantially insoluble in water; supplying heat to said treatmentliquid so as to cause said water in said electrode to evaporate;collecting and condensing all of the vapor of said water along withwhatever vapor may be contributed by evaporation of said treatmentliquid; returning all of the condensate produced by said collecting andcondensing steps into said treatment liquid in which said electrode isimmersed at a level spaced below said electrode in a closed circulatorymanner; and allowing the water in said condensate to settle; whereby thelevel of said treatment liquid in which said electrode is immersedremains substantially constant throughout the entire course of saidevaporation and said electrode is maintained continuously immersed insaid treatment liquid and thereby protected against exposure to theatmosphere.

11. The method of drying a water containing charged porous batteryelectrode, which comprises the steps of: immersing said electrode in afirst volatile treatment liquid which is substantially insoluble inwater and which contains a wetting agent for causing said firsttreatment liquid to displace said water from said electrode; removingsaid first treatment liquid substantially entirely from said electrodeby evaporation; immersing said electrode in a second volatile treatmentliquid which is soluble in water for dissolving undisplaced waterremaining in said electrode, said second treatment liquid having asubstantially non-volatile coating substance dissolved therein; andremoving substantially all of said second treatment liquid from saidelectrode by evaporation leaving a protective layer of said coatingsubstance deposited on said electrode.

12. The method according to claim 11, comprising the further step ofcollecting and condensing the vapor of said first treatment liquid forre-use; collecting and condensing the vapor of said second treatmentliquid along with water vapor; and distilling the condensate obtained bysaid lastnamed condensing step to recover said second liquid therefromfor re-use.

References Cited in the file of this patent UNITED STATES PATENTS1,799,248 Reinhardt Apr. 7, 1931 FOREIGN PATENTS 201,750 Germany Aug. 1,1907

10. THE METHOD OF DRYING A WATER-CONTAINING, CHARGED POROUS BATTERYELECTRODE WHILE SIMULTANEOUSLY PROTECTING THE ELECTRODE AGAINST ATTACKFROM THE OXYGEN OF THE ATMOSPHERE, COMPRISING THE STEPS OF: IMMERSINGSAID ELECTRODE IN A TREATMENT LIQUID HAVING A BOILING POINT HIGHER THANTHAT OF WATER, A SPECIFIC GRAVITY LESS THAN THAT OF WATER, AND WHICH ISSUBSTANTIALLY INSOLUBLE IN WATER; SUPPLYING HEAT TO SAID TREATMENTLIQUID SO AS TO CAUSE SAID WATER IN SAID ELECTRODE TO EVAPORATE;COLLECTING AND CONDENSING ALL OF THE VAPOR OF SAID WATER ALONG WITHWHATEVER VAPOR MAY BE CONTRIBUTED BY EVAPORATION OF SAID